The Illuminating Engineering Society of North America recommends a 30-50 foot-candle (fc) range for ambient (general) office lighting, yet most workspaces are lit to 60 fc on average. Over-lighting can cause unnecessary eye strain for occupants and higher energy costs for companies. Under-lighting can also cause unnecessary eye strain and provide a less pleasing or less productive workspace.
Further, in large or open workspaces, whether the spaces are commercial, industrial, retail, or public, such as office buildings, warehouses, schools, malls, and the like, the amount of light provided within the space is impacted not only by the artificial lighting system installed in the space but also by the amount of natural light entering the space through windows, doors, and skylights.
However, the amount of natural light entering a space can vary greatly based on the time of day, the time of year, and the weather conditions at any point in time. Further, the location and angle of the natural light entering the space can also vary greatly based on those same factors.
Many different types of lighting-control system have been developed to help reduce energy waste and take advantage of natural light conditions, while still providing a productive and pleasing visual environment. Lighting control means having the ability to illuminate a space where and when it is needed and the power to conserve energy when and where illumination is not needed. To accomplish this, controls can ideally provide the right amount of light where and when it is needed—either automatically or at a user's discretion.
Lighting controls, such as dimming features, can reduce lighting energy consumption and produce energy savings, especially if the dimming is responsive to the amount of natural light entering a space. Dimming a light fixture saves energy when operating a light source and also allows a user to adjust the intensity of the light source to a desired level. Many indoor and outdoor facilities, such as homes, buildings, parking lots, and streets, include light source dimming circuits.
The most common use of dimming is for indoor applications, such as for dimming a room. Dimming is also ideally suited to energy management applications, such as daylight harvesting. For example, automated dimming systems can provide a smooth and unnoticeable transition to lower electric light levels as daylight levels increase, all while maintaining the desired light level, to produce significant lighting energy savings.
For example, a time-based dimming controller can turn on a lighting fixture at dusk, dim the lighting fixture at one or more predetermined times to preset amounts, return the lighting fixture to full brightness at 5 a.m., and turn off the lighting fixture at dawn, offering 20-30 percent energy savings above normal photocell operation.
Photo sensors can also be used to good effect to dim light fixtures in a workspace based on detecting ambient light levels. However, as stated above, in larger workspaces and open areas, the amount of ambient light can vary significantly in different parts of the workspace, based on proximity or distance from natural light sources and based on amount of natural light coming into the workspace at different times of the day, at different times of the year, and based on variable weather conditions, which can change frequently throughout a single day.
However, merely adding more photo sensors to different banks of lights within such large workspace does not necessarily create a pleasing or uniform lighting environment. Nor does it address the end user's needs, which may be to have higher or lower lighting in selected areas of the workspace.
There is thus a need to enable an end user to limit the range and hence the dimming level of selected lighting fixtures or banks of lights within a workspace. This is important for users who want a more uniform “ceiling” appearance throughout the entire workspace or who want a generally uniform ceiling appearance, but need more customized lighting in selected areas of the workspace. An example would be an installation with multiple photocells installed. The fixtures near windows could be noticeably dimmer than fixtures further away. Thus, it may be desirable for the end user to be able to set customizable dimming or brightness levels to keep the light level between various fixtures closer in light level even as the ambient light level within the space varies.
These and many other needs are addressed by the circuits, methods, devices, and systems for controlling the brightness level of a light electrically coupled with a dimmable driver, such as a dimming ballast or LED driver, as described in greater detail hereinafter.